Overrunning bi-directional clutches are known, see for example U.S. Pat. Nos. 6,409,001; 7,004,875; and 7,037,200. Such clutches are mounted between two coaxial shafts and are used to transfer power between the two shafts. The clutch is fixed to a first shaft and selectively engages with the second shaft so as to transfer power between the two shafts. Typically, the first shaft is the power input shaft and typically, the first shaft is also the inner shaft of the two shafts. The output shaft or second shaft can be a geared wheel.
Overrunning bi-directional clutches comprise a fixed race, a slipper race, cylindrical rollers which are housed between the two races and an actuator. The fixed race and the slipper race are coaxial cylindrical rings with opposing faces. Each of the opposing faces has concave bearing surfaces which define pockets. Each pocket houses a roller.
The slipper race has an axial groove or slit that extends both radially and axially through the race. The slit allows the slipper race to move radially under force and the memory inherent in the material from which the slipper race is made allows the race to return to a rest position once the force is withdrawn. The fixed race is mounted onto the first shaft while the slipper race is spaced in close proximity to the second shafts such that when the slipper race moves radially, it the second race, thereby transferring power between the two shafts. Once the force is removed from the slipper race, it returns to its rest position and no longer engages the second shaft. The rest position is generally referred to as the “freewheeling mode” or the first mode of operation of a clutch, while the engaged position when the slipper race engages the second shaft is referred to as the “blocked mode” or second mode of operation for the clutch.
The actuator is used to maintain the clutch in the freewheeling mode and to move the clutch to the blocked mode. Typically, the actuator is a radial mounted moveable pin which is fixed to the fixed race and retractable from the slipper race. When the actuator engages both races the two races are coupled and the clutch is in the freewheeling mode. In the freewheeling mode, the opposing concave bearing surfaces are aligned with each other and the rollers rest in the bottom of each of the opposing concave surfaces. When the actuator pin is withdrawn from the slipper race, the two races move relative to one another and the rollers move out of the bottom of the opposing concave surfaces and rise up along diagonally opposing surfaces of the pocket so as to force the slipper race to move radially and to engage the second shaft.
One of the problems with overrunning bi-directional clutches is that once the actuator is moved to transfer the clutch from the freewheeling mode to the blocked mode, the clutch reacts very quickly and the overall time period is on the order of 10 to 25 milliseconds. For shafts traveling at high speeds, this shift can cause large noises, clunking and heat because the second shaft is essentially at rest and must be brought up to the speed of the first shaft instantaneously.